1. Field of the Invention
The present invention relates to load storage apparatus or equipment for storing loads in a clean room or the like.
2. Brief Description of the Prior Art
A conventional load storage apparatus includes a rack with shelves or other load supports, each of which can support a cassette containing a number of wafers or liquid crystal panels. The shelves have pins for positioning the cassettes supported on the shelves. The cassettes have holes for engaging with the pins. The engagement prevents the cassettes on the shelves from shifting out of position in such a manner that the cassettes cannot be taken normally out of the storage apparatus. The engagement also prevents the cassettes on the shelves from falling due to the vibration of the shelves during the operation of the storage apparatus, or due to an earthquake, for example.
The storage apparatus also includes a transferrer for loading and unloading the rack. The transferrer includes a carrier, which is designed to move for constant distances in order to transfer the cassettes to and from the shelves.
The rack may be three-dimensional, with the shelves large in number. In this case, initial errors in size of the rack, installation or fixation errors in horizontal and/or vertical accuracy of the rack, and/or other errors may delicately or slightly vary the positions of the positioning pins of the shelves relative to the carrier of the transferrer and/or the distance between each of the pins and the carrier. The variation may prevent the cassette holes from engaging normally with the shelf pins so that the cassettes can be normally loaded and unloaded. Therefore, before the rack is loaded with cassettes or unloaded, an operator must make adjustments by causing the transferrer to operate for each of the shelves, measuring the proper distance for which the carrier moves relative to each of the shelves, and recording the measured distances.
The adjustments require much time and labor, and operators different in skill may make various adjustments.